Cancer is the commonest cause for death among all of the causes for death, and therapies carried out therefor at present are mainly surgical treatment, which may be carried out in combination with radiotherapy and/or chemotherapy. In spite of the developments of new surgical methods and discovery of new anti-cancer agents in recent years, treatment results of cancers have not been improved very much so far except for some cancers. In recent years, by virtue of the development in molecular biology and cancer immunology, cancer antigens recognized by cytotoxic T cells reactive with cancers, as well as the genes encoding cancer antigens, were identified, and expectations for antigen-specific immunotherapies have been raised.
In immunotherapy, in order to reduce side effects, the peptide or protein to be recognized as the antigen needs to be hardly present in normal cells, and to be specifically present in cancer cells. In 1991, Boon et al. of Ludwig Institute in Belgium isolated a human melanoma antigen MAGE 1, which is recognized by CD8-positive T cells, by a cDNA-expression cloning method using an autologous cancer cell line and cancer-reactive T cells (Non-patent Document 1). Thereafter, the SEREX (serological identifications of antigens by recombinant expression cloning) method, wherein tumor antigens recognized by antibodies produced in the living body of a cancer patient in response to the patient's own cancer are identified by application of a gene expression cloning method, was reported (Patent Document 1, Non-patent Document 2), and several cancer antigens have been isolated by this method. Using a part of the cancer antigens as targets, clinical tests for cancer immunotherapy have started.
On the other hand, as in human, a number of tumors such as mammary gland tumor and squamous cell carcinoma are known in dogs and cats, and they rank high also in the statistics of diseases in dogs and cats. However, no therapeutic agent, prophylactic agent or diagnostic agent effective for cancers in dogs or cats exists at present. Since most tumors in dogs and cats are realized by their owners only after the tumors grew larger due to the progression, their visit to the hospital is already too late, and even if they receive surgical excision or administration of a human drug (an anticancer drug or the like), they often die shortly after the treatment. Under such circumstances, if therapeutic agents and prophylactic agents for cancer effective for dogs and cats become available, their uses for dog cancers are expected to be developed.
Stearoyl-CoA desaturase 1 (SCD1) introduces a double bond to the C9-C10 position of a saturated fatty acid. Preferred substrates for the enzyme are palmitoyl-CoA (16:0) and stearoyl-CoA (18:0), and these are converted to palmitoleoyl-CoA (16:1) and oleoyl-CoA (18:1), respectively. The obtained monounsaturated fatty acid can then be used in vivo for preparation of phospholipids, triglycerides and cholesteryl esters. Further, various cancers such as liver cancer, esophagus cancer and colon cancer show increased expression of SCD1, and it has been reported that inhibition of the function of SCD1 with siRNA or a low-molecular-weight compound causes suppression of the cell growth or induction of apoptosis (Non-patent Documents 3, 4 and 5). However, there is no report suggesting that SCD1 protein has immunity-inducing activity against cancer cells and hence that the protein is useful for treatment or prophylaxis of cancer.